Geoengineering is the deliberate and large-scale intervention in the Earth’s climatic system with the aim of reducing global warming. The discipline divides broadly into two categories- carbon dioxide removal and solar radiation management.
- Carbon dioxide removal addresses a cause of climate change by removing one of the greenhouse gases from the atmosphere.
- Solar radiation management attempts to offset effects of greenhouse gases by causing the Earth to absorb less solar radiation.

The Intergovernmental Panel on Climate Change (IPCC) concluded in 2007 that geoengineering options remained largely unproven.

Geoengineering has been proposed as a potential third option for tackling global warming, alongside mitigation and adaptation. Scientists do not typically suggest geoengineering as an alternative to emissions control, but rather an accompanying strategy.[6] Reviews of geoengineering techniques have emphasised that they are not substitutes for emission controls and have identified potentially stronger and weaker schemes.

There are no known large-scale geoengineering projects except one conducted outside the scientific mainstream by Russ George. Almost all research has consisted of computer modelling or laboratory tests, and attempts to move to real-world experimentation have proved controversial. Some limited tree planting and cool roof projects are already underway. Ocean iron fertilization has been given small-scale research trials. Field research into sulphur aerosols has also started.

Various criticisms have been made of geoengineering and some commentators appear fundamentally opposed. Some have suggested that the concept of geoengineering presents a moral hazard because it could reduce the political and popular pressure for emissions reduction. Groups such as ETC Group and individuals such as Raymond Pierrehumbert have called for a moratorium on deployment and out-of-doors testing of geoengineering techniques. The full effects of various geoengineering schemes are not well understood.